The present invention relates to a sewing machine which automatically controls a lower thread tension.
There have been proposed many automatic methods of controlling upper thread tension or a supply amount in response to type of fabrics, threads, needle amplitude widths or fabric feeds, so that an upper thread and a lower thread cross appropriately in a fabric under stitching to provide satisfactory stitches. However, especially in thin fabric, due to fabric shrinkage and other inconveniences, it has not been always sufficient to adjust the upper thread tension only.